adding decision making section

https://gitlab.com/gitlab-com/peopleops/issues/313 In this MR:

In preparation for Decision Making training I have done the following:

1. Taken existing decision content and created a Making Decisions section on the leadership page
2. Added some content from Re:work with Google
3. Added an article from the Harvard Business Review
4. Assigned to Barbie for further review. Barbie has added some additional wording to the Making Decisions section.

Once the training has been delivered I will do another MR to include:

1. Additional points from the training
2. Add the slide deck and video to the courses page and link it to this section on the leadership page.